“Why do some potting soils turn green? What is it, and how can I avoid this from happening? Thank you.” Question from Angela of Taylor, Michigan
Answer: Any potting soil can turn green. That is because it is algae, or more rarely moss, that is causing the green color, and excess water on the soil surface is the culprit. A green layer on your soil means too much water. When you water to the point where the surface soil is kept wet, this invites the growth of algae. Algae and algal spores can exist in soil, water, or even air, so “clean” soil won’t keep the problem away. The best way to avoid algae is to clean up and change your watering practices.
Cleaning Up Algae in the Pot
Start by skimming off the first couple of inches of greenish potting mix on your pot tops, and refresh with new potting mix. We recommend replenishing with Black Gold All Purpose Potting Mix. It is also important that you have pots that drain well and bottom saucers for watering. If you need to upgrade your plant’s pots, it’s worth it. Pots like these will enable bottom watering.
Watering to Avoid Algae
Allow the top two inches of potting soil to become dry between watering. This will halt algal growth. Another method is to water your plants from the bottom saucer only when they need it.
To learn more about best-practices for plant watering, read our article How to Water House Plants.
Black Gold Horticulturist
Plants are the lens Jessie views the world through because they’re all-sustaining. (“They feed, clothe, house and heal us. They produce the air we breathe and even make us smell pretty.”) She’s a garden writer and photographer with degrees in both horticulture and plant biology from Purdue and Michigan State Universities. Her degrees were bolstered by internships at Longwood Gardens and the American Horticultural Society. She has since worked for many horticultural institutions and companies and now manages communications for Sun Gro Horticulture, the parent company of Black Gold. Her joy is sharing all things green and lovely with her two daughters.
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